Sensorless Control with High Inertia

25. June 2013

Celeroton‘s converters allow for sensorless motor control. The higher the interia, the bigger the challenge for our development engineers.

What are the biggest challenges?

Several applications with high rotational speeds such as beam choppers, flywheels, optical systems, test benches or special machining spindles show large moments of inertia. This results in the following challenges:

Acceleration time is very high

The reference current (output of the speed controller) is saturating during the entire acceleration

The actual speed control modulation occurs in a narrow rotational speed range

Which additional difficulties might arise?

If sensorless control starts from a minimal rotational speed, motors might fall out of synchronization t during ramp up because of the missing position signal. This has to be avoid, especially with long acceleration times.In addition, several applications require the use of magnetic bearings. In this case sensorless control is desirable or necessary because encoders and Hall sensors are not precise enough in case of radial displacement of the rotor. Furthermore, the large magnetic air gaps leads to remarkably lower inductances, and low rotor losses are required to avoid over temperatures.

Small rotor losses even at high rotational speeds and low inductive motors due to optimal converter modulation

Adjustable time constants and filters

Adjustment of bandwidths possible

Filter systems can be added

External speed controller possible

Adjustment of reference moment with adjustment of reference current through converter interfaces

Field orientation/commutation of currents still by sensorless rotor position detection

How are these advantages adopted to unique customer applications?

High moments of inertia often require custom-specific modifications of the control. For this, we offer consulting and application engineering services for our clients. Customer requirements range from synchronizing the commutation with external signals, specific starting sequences and acceleration ramps to the estimation of the load torque at runtime.

Control structure and interface possibilities of Celeroton’s CC converter family